It is widely known (for example, Patent Literature 1 and the like) that maleic acid-modified polypropylene (hereinafter sometimes abbreviated as “MAPP”) is used as a compatibilizer or an interface-reinforcing agent in composite materials comprising cellulose-based microfibrillated plant fibers and polyolefins such as polypropylene (hereinafter sometimes abbreviated as “PP”).
Additionally, the Examples of Patent Literature 2 disclose a composite material obtained from microfibrillated plant fibers containing lignin, PP, and MAPP. Further, the Examples of Patent Literature 3 disclose a composite material comprising lignocellulosic fibers, PP, and MAPP. In these composite materials, MAPP and lignin presumably function as interface reinforcing agents between PP and microfibrillated plant fibers, or between lignocellulosic fibers. However, because polyolefins such as PP are usually highly hydrophobic, when such a material is mixed with plant fibers mainly comprising highly hydrophilic cellulose, the uniform dispersibility and the interfacial interaction between these components are not sufficient even with the above methods, and it has been difficult to obtain a molded article with high strength.